1. Field of the Invention
The present invention relates to an oscillation type gyro sensor for detecting rotational angular velocity of an object, a control circuit thereof, an electronic apparatus mounted with the oscillation type gyro sensor, and a method of manufacturing an oscillation type gyro sensor.
2. Description of the Related Art
As commercially used angular velocity sensors, so-called oscillation type gyro sensors have been widely used. An oscillation type gyro sensor is a sensor having a cantilevered oscillator that oscillates at a predetermined resonance frequency and a piezoelectric element that detects the Coriolis force that occurs due to an influence of an angular velocity so as to detect the angular velocity.
An oscillation type gyro sensor has advantages of, for example, simple mechanism, short activation time, and low manufacturing cost. Oscillation type gyro sensors are mounted in electronic apparatuses such as video cameras, virtual reality devices, and car navigation systems for sensors that perform shake detection, motion detection, and direction detection, respectively.
In recent years, as electronic apparatuses in which an oscillation type gyro sensor is mounted have been downsized and have had improved functions, needs of downsizing and advanced functions of the oscillation type gyro sensors have become strong. For example, to satisfy the needs of multi-functions and downsizing of an electronic apparatus, an oscillation type gyro sensor is mounted on a single circuit board together with other sensors. To accomplish the downsizing of the electronic apparatus, a technique called the MEMS (Micro Electro Mechanical System) that forms a structure on an Si substrate using a thin film process and a photolithography technique for semiconductors has become common.
In the meantime, there has been a problem in that, depending on the environment in which the oscillation type gyro sensor is used, particularly depending on temperature, the characteristics of the oscillation type gyro sensor change.
To be specific, the oscillation type gyro sensor is driven by a constant drive signal which is set to have a value of a resonance frequency of an oscillator. In the case that the drive signal has a constant value, it is considered that detection sensitivity is to be constant regarding a configuration of a circuit of the oscillation type gyro sensor. However, due to the change of temperature, the detection sensitivity tends to change so as to be in proportion with the change of temperature.
To solve the problem as described above, there is disclosed an oscillation type gyro sensor provided with a circuit for allowing a detection signal output from a detection electrode of an oscillator to be constant (for example, see Japanese Patent Application Laid-Open No. Hei 9-292231, paragraphs 0023 and 0016, FIG. 1, hereinafter this document is referred to as Patent Document 1).
In Patent Document 1, two detection electrodes (16a, 16b) of an oscillator (12) output current signals. I-V converter circuits (24, 26) convert the current signals to voltage signals. An addition circuit (28) adds the voltage signals. An oscillation circuit (34) and a monitor circuit (40) control the signal output from the addition circuit (28) to be constant. In other words, the voltage of the drive signal output from an AGC (Automatic Gain Controller) circuit (38) is controlled such that the output signal voltage from the addition circuit (28) is always constant. As a result, even when characteristics of the oscillator (12) change depending on temperature, detection sensitivity can be kept constant.